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Application of modified Manning formula in the determination of vertical profile velocity in natural rivers

S.Song, B.Schmalz, J. X.Zhang, G.Li, N.Fohrer

Available Online 3 March 2016, nh2016131; DOI:10.2166/nh.2016.131

S. Song

School of Geographic and Oceanic Science, Nanjing University, Nanjing, China E-mail: ssong@hydrology.uni-kiel.deDepartment of Hydrology and Water Resources Management, University of Kiel, Kiel, Germany

Abstract

Seldom studied before, the vertical profile velocity is indicative to the flood process and nutrient transportation process. In this paper, a substitution of cross section hydraulic radius with vertical depth was made to the Manning formula which was then applied in the vertical profile velocity determination. Simultaneously, the determination accuracy and its relationship with hydraulic conditions were discussed, based on the 1050 vertical profiles sampled from 140 cross sections in flood and moderate level season. The observations show that: (1) the modified Manning formula provide a simplified approach for vertical profile velocity determination with acceptable accuracy; (2) the fitting quality of the profile velocity from the middle region of cross section and flood season were higher than that from near the bank or moderate level season. The coefficient of determination (R2) of the regression for moderate level season and flood season were 0.55 and 0.58, while the Nash–Sutcliffe coefficients were 0.64 and 0.82, respectively; (3) analysis of determination error and the coefficient of variation showed a positive correlation with river aspect ratio. This seems to suggest that the modified Manning formula tends to be more applicable in narrow and deep rivers. More measurements from rivers or channels with high aspect ratio would be meaningful for future research.